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No description available.

Water and wastewater conveyance research is steeply based in advancements of numerical methods and models. Design engineers need more than refinements in analysis methods to evolve the standards of practice and the related design guidelines. In an effort to improve the design efficiency and operating reliability of pipeline systems, design guidelines have been developed to enfold the various technological advancements and elevate the standard of care used in the pipeline design process. In this respect, the guidelines have been successful. However, design engineers, manufacturers, and owners have developed a level of dependency on the success of the guidelines. The guidelines, which were developed as and are clearly still held to be by the various publishing associations, a minimum standard of care, have become the default standard of care. Such statements are, of course, gross generalizations, but this thesis is dedicated to move the standard of care forward through an integrated design approach that provides a roadmap to inter-relate the independent design guidelines into a composite design approach based on hydrodynamic loading. Hydrodynamic loading introduces of a temporal parameter into the design process. With the temporal parameter this work demonstrates how the consideration of both the frequency and the influence of acceleration head on the magnitude of the hydraulic loading can be used to integrate and evolve the individual component designs into a more efficient, cost effective, reliable composite design result. With a temporal parameter present in design, many opportunities present themselves to advance the current design procedures outlined in the present design guidelines. This thesis identifies some of the present shortcomings found in the modern pipeline and appurtenance design standards and introduces a recommended path forward. Specific changes to the present standards are proposed in this work and a unique analysis procedure to identify the failure potential of cement mortar lining has been developed. Introducing the integrated design approach will allow for a significant evolution to the present standard of practice in water and wastewater conveyance system designs.

Water and wastewater conveyance research is steeply based in advancements of numerical methods and models. Design engineers need more than refinements in analysis methods to evolve the standards of practice and the related design guidelines. In an effort to improve the design efficiency and operating reliability of pipeline systems, design guidelines have been developed to enfold the various technological advancements and elevate the standard of care used in the pipeline design process. In this respect, the guidelines have been successful. However, design engineers, manufacturers, and owners have developed a level of dependency on the success of the guidelines. The guidelines, which were developed as and are clearly still held to be by the various publishing associations, a minimum standard of care, have become the default standard of care. Such statements are, of course, gross generalizations, but this thesis is dedicated to move the standard of care forward through an integrated design approach that provides a roadmap to inter-relate the independent design guidelines into a composite design approach based on hydrodynamic loading. Hydrodynamic loading introduces of a temporal parameter into the design process. With the temporal parameter this work demonstrates how the consideration of both the frequency and the influence of acceleration head on the magnitude of the hydraulic loading can be used to integrate and evolve the individual component designs into a more efficient, cost effective, reliable composite design result. With a temporal parameter present in design, many opportunities present themselves to advance the current design procedures outlined in the present design guidelines. This thesis identifies some of the present shortcomings found in the modern pipeline and appurtenance design standards and introduces a recommended path forward. Specific changes to the present standards are proposed in this work and a unique analysis procedure to identify the failure potential of cement mortar lining has been developed. Introducing the integrated design approach will allow for a significant evolution to the present standard of practice in water and wastewater conveyance system designs.

This study investigated the changes in leachate composition and clogging evolution in leachate transmission pipes and the use of methanogenesis as a leachate treatment alternative for Bioreactor landfills, by using pilot-scale and laboratory studies. The pilot-scale study consisted of a research station built at Brady Road Landfill, housing sixteen HDPE pipes of three different diameters, conveying leachate intermittently at eight different Reynolds numbers, under reasonably controlled conditions. The pipes were tested for leachate degradation, clogging evolution and hydraulic impairment over time. The laboratory studies carried out tested (1) the effect of turbulence intensity and temperature on leachate degradation and clogging effects and (2) biological pretreatment of leachate prior to injection into a bioreactor cell. The pilot study results showed that under the conditions tested, pipes developed a significant amount of organic and inorganic clog material in less than a year of operation. Since limited quantities of fresh leachate (approx. 3 m3) were used during each leachate degradation analyses, the anticipated effects of clogging in a full scale injection system are expected to be more pronounced, which can negatively impact the long-term hydraulic performance, operation, and service life of a Bioreactor Landfill. The first laboratory study showed that increasing the turbulent energy dissipation rate caused greater amounts of CO2 evolution from the leachate, and temperature increase had an impact on dissolved Ca2+ under atmospheric conditions, affecting clog development. The second and third laboratory studies showed that performing leachate methanogenesis reduces organic (COD, VFA) and inorganic (Ca2+, ISS) clog constituents within the leachate However, the rate of methanogenesis was influenced by the ratio of acetate and propionate. It is suggested that if leachate undergoes methanogenesis in a separate leachate digester prior to re-injection into a bioreactor waste cell, it may protect the pipes and other engineered landfill systems against clogging and its detrimental effects, while allowing for CH4 recovery. However, blending of leachates from different wells or cells prior to the methanogenic digester may be needed to balance the variable concentrations and ratios of acetate and propionate over time from different landfill wells and cells.

No description available.

The need for optimal air vessel sizing tools, in protecting large pipe networks from undue transient pressures is well known. Graphical and other heuristic methods reported in literature are limited to sizing the air vessels for simple rising mains. Although attempts have been made to utilize optimization techniques, they have been largely unsuccessful due to their impractical computational requirements. This research work proposes a robust framework for developing surge protection design tools and demonstrates the usefulness of the framework through an example air vessel sizing tool. Efficiency and robustness of the proposed framework are demonstrated by developing a design aid for air vessel sizing for protecting large pipe network systems against excessive high pressures generated by rapid valve closures. The essence of the proposed framework is in identification of key transient response parameters influencing air vessel parameters from seemingly unmanageable transient response data. This parameterization helps in exploiting the similarity between transient responses of small pipe networks and sub-sections of large pipe networks. The framework employs an extensive knowledgebase of transient pressure and flow scenarios defined from several small network models and corresponding optimal air vessel sizes obtained from a genetic algorithm optimizer. A regression model based on an artificial neural network was used on this knowledgebase to identify key parameters influencing air vessel sizes. These key parameters were used as input variables and the corresponding air vessel parameters as output variables to train the neural network model. The trained neural network model was successfully applied for large complex pipe networks to obtain optimal air vessel sizes for transient protection. The neural network model predictions were compared with optimal air vessel parameters to assess the efficacy of the proposed framework. The validity and limitation of the design aid developed and areas in the framework that need further research are also presented. The proposed frame work requires generation of hundreds of optimization data for small and simple network systems which is a daunting task since genetic algorithm-based optimization is computationally expensive. Selection of a numerically efficient and sufficiently accurate transient analysis method for use inside a genetic algorithm based optimization scheme is crucial as any reduction in transient analysis time for a network system would tremendously reduce the computational costs of bi-level genetic algorithm optimization scheme. This research work also demonstrate that the Wave Plan Method is computationally more efficient than the Method of Characteristics for similar accuracies and the resulting savings in computational costs in the transient analysis of pipe networks and subsequently in the genetic algorithm based optimization schemes are significant.

Fluid flow network simulation codes are commonly used as a design and analysis tool for many engineering problems such as gas distribution networks, power plants and heat pumps. Two formulations of conservation of momentum have been widely applied in fluid flow network simulation models namely those based on static pressure and those based on total pressure. The total pressure formulations are convenient in that they eliminate the difficulties associated with the calculation of the convective terms and components such as pipe junctions are treated in a straightforward manner based on total pressure losses. However, the different formulations of total pressure for compressible and incompressible flow require different formulations of the momentum conservation equation, which is inconvenient for implementation in a generic network simulation code. In this thesis a united total pressure formulation is first derived which is valid for all fluids and therefore eliminates the inconvenience of switching between the compressible and incompressible formulations. A non-iterative method for the solution of the non-isothermal discretised equations based on the total pressure formulation is then introduced and consistency is illustrated. The method appears to be very stable for subsonic flows, while rapid steady state convergence is observed. A systematic comparison is also done with traditional static pressure based methods and the similarities and differences between the two formulations are illuminated. The different time scales involved in the simulation of transient flow in fluid networks are problematic when conventional fixed time step methods are used for time-wise integration. The time scales associated with acoustic and kinematic wave phenomena as well as storage effects can differ by orders in magnitude. This thesis also presents a simple adaptive time step algorithm which can be readily used in conjunction with all the commonly used first order methods for fluid flow networks. Two test problems are selected to demonstrate the efficiency and savings obtained with this procedure. The adaptive time step algorithm correctly selects appropriate time steps for all phenomena and significant computational savings are observed for accurate integration. In addition, a procedure is implemented which automatically selects the appropriate integration method. The resulting algorithm is a fully adaptive algorithm which switches between a fully implicit method and a semi-implicit method. Two test problems are once again used to demonstrate the efficiency and savings. The fully adaptive algorithm correctly selects appropriate methods for all phenomena and significant additional computational savings are observed. / Thesis (PhD (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

Fluid flow network simulation codes are commonly used as a design and analysis tool for many engineering problems such as gas distribution networks, power plants and heat pumps. Two formulations of conservation of momentum have been widely applied in fluid flow network simulation models namely those based on static pressure and those based on total pressure. The total pressure formulations are convenient in that they eliminate the difficulties associated with the calculation of the convective terms and components such as pipe junctions are treated in a straightforward manner based on total pressure losses. However, the different formulations of total pressure for compressible and incompressible flow require different formulations of the momentum conservation equation, which is inconvenient for implementation in a generic network simulation code. In this thesis a united total pressure formulation is first derived which is valid for all fluids and therefore eliminates the inconvenience of switching between the compressible and incompressible formulations. A non-iterative method for the solution of the non-isothermal discretised equations based on the total pressure formulation is then introduced and consistency is illustrated. The method appears to be very stable for subsonic flows, while rapid steady state convergence is observed. A systematic comparison is also done with traditional static pressure based methods and the similarities and differences between the two formulations are illuminated. The different time scales involved in the simulation of transient flow in fluid networks are problematic when conventional fixed time step methods are used for time-wise integration. The time scales associated with acoustic and kinematic wave phenomena as well as storage effects can differ by orders in magnitude. This thesis also presents a simple adaptive time step algorithm which can be readily used in conjunction with all the commonly used first order methods for fluid flow networks. Two test problems are selected to demonstrate the efficiency and savings obtained with this procedure. The adaptive time step algorithm correctly selects appropriate time steps for all phenomena and significant computational savings are observed for accurate integration. In addition, a procedure is implemented which automatically selects the appropriate integration method. The resulting algorithm is a fully adaptive algorithm which switches between a fully implicit method and a semi-implicit method. Two test problems are once again used to demonstrate the efficiency and savings. The fully adaptive algorithm correctly selects appropriate methods for all phenomena and significant additional computational savings are observed. / Thesis (PhD (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013